Problem: Solve for $k$ : $18 = 23 + k$
Explanation: Subtract $23$ from both sides: $ \begin{eqnarray} \\ \hphantom{18 {- 23}} &\hphantom{=}& \hphantom{k} \\ 18 &=& 23 + k \\ \\ {-23} && {-23} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ 18 {- 23} &=& k \\ \end{eqnarray} $ Simplify. $ k = -5$